There have been previously known apparatus and methods for sorting defective items from acceptable items by using machine vision techniques. In the agricultural product inspection industry, the definition of a defective item varies from product to product. For example, a black spot on a potato chip or brown rot on a green bean are considered defects. The above defects are characterized by imperfections in the color or texture of the item. In the pickle processing industry, one common defect is characterized as a pickle with a hole or a slit in the middle. This kind of defect results in imperfections in the shape, rather than the color of the item.
Existing methods for removing defects in food products rely on color or texture to classify defects. For example, U.S. Pat. No. 5,085,325 of Jones et al. for COLOR SORTING SYSTEM AND METHOD, assigned to the assignee of the present invention, describes a sorting system having a color camera for inspecting items as they are moved or propelled through an inspection zone by a conveyor belt. Color video data from the camera are digitized and used to address a lookup table containing criteria representing acceptable and rejectable colors. When an item including a defective color is detected by the camera, the location of the defect is stored in a memory for subsequent rejection downstream of the camera. Conveyor belts typically move with sufficient speed to propel items off the end of the belt where a bank of air ejectors, triggered in response to stored defect data, are positioned to deflect defective items toward a rejection conveyor, while allowing acceptable items to fly undeflected toward an acceptance conveyor. Such a system is quite effective at sorting items based on the color and size of defects, but cannot detect unacceptably shaped articles having an otherwise acceptable color.
In another example, U.S. Pat. No. Re. 33,357 of Randall for OPTICAL INSPECTION APPARATUS FOR MOVING ARTICLES, describes a system for inspecting and cutting defects from french fried potatoes and other elongated articles. In the system of Randall, video data representing grey-scale levels corresponding to light levels reflected from items being inspected are digitized and presented to shade detectors, one for light shade defects and one for dark shade defects. Counters accumulate the number of consecutive light and/or dark shade defects detected to determine the size of such defects. When preset size thresholds are exceeded, the defect is excised from the item by a rotary cutter knife. Such a system is capable of differentiating between certain large, light shade defects and certain small, dark shade defects, but cannot detect background-colored shade defects such as holes.
What is needed, therefore, are an apparatus and a method for classifying shape related defects, such as holes of predetermined sizes.